Conductivity sensors are normally provided in order to detect the actual conductivity of fluids, such as gases or liquid solutions. The general principle is based on the fact that the electrical conductivity is a very specific property of fluids. A change in composition or temperature will provide a change in conductivity. Hence, by measuring the conductivity variations within a system may easily be detected.
Different methods for measuring conductivity have been proposed, in which one includes the provision of four concentrically arranged electrodes. An alternating current is supplied to the outer pair of electrodes, whereby the potential of the inner pair of electrodes is probed as a measure of the actual conductivity of the media surrounding the electrodes.
It has been suggested to use conductivity measurements for determining the presence of leaks in a double membrane diaphragm pump, as e.g. been described in SE1251496-4 by the same applicant. Such pump, which in general is a piston pump used for hygienic applications such as homogenizers, utilizes a chamber formed between two membranes forming a seal between a liquid product, i.e. a hygienic side, and a hydraulic pressure source, i.e. a non-hygienic side. In order to detect a leakage a conductivity sensor is arranged in contact with the fluid between the two membranes. Hence, should a membrane be damaged whereby hydraulic oil is allowed to enter the hygienic side the conductivity will change, whereby an alarm may be triggered for initiating service or replacement of the membranes.
In the above application the pump is operated to increase the pressure from approximately 3 bar up to 250 bar during the course of each pump/suction stroke. The pressure in the pump chamber thus increases from a low pressure, such as 3 bar, to a high pressure, such as 250 bar in a periodical manner during operation. Even higher pressure may also be provided. Further to this elevated temperatures up to 140° C. may be provided, especially if the pump is arranged adjacent to heat treatment equipment.
It is required that the conductivity sensor is constructed to withstand the harsh environment in view of temperature and pressure inside the chamber. Further, the conductivity sensor should be operational for determining changes in the conductivity as such occur inside the pressure chamber.
In view of above, there is a need for an improved conductivity sensor for use in high pressure and high temperature applications. Further, there is a need for a high pressure pump for use in hygienic application having means for leakage detection.